Image draw method option

This option replaces previously added GPU limit
option, which became tricky to follow after GLSL
display space conversion.

There're 4 modes available:
- AUTO which will try to guess which mode is
  best to use.
  Currently It'll try using GLSL and if it fails,
  will fallback to 2D textures.
  Probably it'll make sense checking on whether
  2D textures works well but currently such behavior
  shall be sufficient.
  Later we could make this method smarter (for example
  don't try to use GLSL on certain GPU or so).
- GLSL will currently behave the same way as AUTO,
  but it is intended to always try using GLSL
  (unless it can not be used because of existing
  limitation of dither and RGB curves).
- 2D Textures will use CPU-based color space conversion
  and use OGL 2D Texture to display the image.
  Image will be displayed in tiles, so there shall be
  no big GPU memory consumption.
- DrawPixels will straightly fallback to glDrawPixels
  without trying to use any fancy GPU stuff.

Hopefully this will also fix
#34943: Blender crashes when resizing the Compositing Screen Window

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55983 954f8c5b-7b00-dc11-b283-0030488c597c